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        <h1 class="title">v-show 和 v-if 遇到的坑</h1>
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                <time datetime="2020-03-09T10:37:11.899Z" itemprop="datePublished" class="page-time">
  2020-03-09
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            <ol class="post-toc"><li class="post-toc-item post-toc-level-1"><a class="post-toc-link" href="#v-show-和-v-if-遇到的坑"><span class="post-toc-number">1.</span> <span class="post-toc-text">v-show 和 v-if 遇到的坑</span></a><ol class="post-toc-child"><li class="post-toc-item post-toc-level-2"><a class="post-toc-link" href="#场景和分析"><span class="post-toc-number">1.1.</span> <span class="post-toc-text">场景和分析</span></a></li><li class="post-toc-item post-toc-level-2"><a class="post-toc-link" href="#总结"><span class="post-toc-number">1.2.</span> <span class="post-toc-text">总结</span></a></li></ol></li></ol>
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        <h1 class="post-card-title">v-show 和 v-if 遇到的坑</h1>
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            <time class="post-time" title="2020-03-09 18:37:11" datetime="2020-03-09T10:37:11.899Z"  itemprop="datePublished">2020-03-09</time>

            
	<ul class="article-category-list"><li class="article-category-list-item"><a class="article-category-list-link" href="/categories/框架/">框架</a><ul class="article-category-list-child"><li class="article-category-list-item"><a class="article-category-list-link" href="/categories/框架/Vue/">Vue</a></li></ul></li></ul>



            
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            <h1 id="v-show-和-v-if-遇到的坑"><a href="#v-show-和-v-if-遇到的坑" class="headerlink" title="v-show 和 v-if 遇到的坑"></a>v-show 和 v-if 遇到的坑</h1><h2 id="场景和分析"><a href="#场景和分析" class="headerlink" title="场景和分析"></a>场景和分析</h2><p>一个文档列表功能，需求是当鼠标移动到文档的 item 上时，显示下载的图标。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">&lt;template lang=&quot;pug&quot;&gt;</span><br><span class="line">    .file-list</span><br><span class="line">        div(v-for=&quot;file in fileList&quot; @mouseover=&quot;overFileId = file.id&quot; @mouseout=&quot;overFileId = &apos;&apos;&quot;)</span><br><span class="line">            div()</span><br><span class="line">              njs-image(:src=&quot;fileIcon&quot; class=&quot;file-icon&quot;)</span><br><span class="line">              span() &#123;&#123;file.name&#125;&#125;</span><br><span class="line">            njs-image(:src=&quot;downLoadIcon&quot; v-if=&quot;overFileId === file.id&quot; @click=&quot;fileDownload(file.path)&quot; style=&quot;width: 20px; height: 20px;&quot; title=&quot;下载&quot;)</span><br><span class="line">&lt;/template&gt;</span><br></pre></td></tr></table></figure>
<p>这时候遇到一个问题，当鼠标移动到下载的图标上的生活，图标消失了(也就是触发了 @mouseout)。经过观察发现这是因为使用了 v-if 是在 overFileId === file.id 条件成立的时候才会去渲染图标的元素，就是说这个元素一开始是不属于注册了 @mouseover 的这个元素的，所以鼠标移上去时会触发 @mouseout。改成使用 v-show 之后就好了，因为 v-show 是一开始就渲染好的元素，然后通过 css 的 ==display: none;== 来控制元素的显示和隐藏，所以不会出现以上的情况。</p>
<h2 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h2><p>v-if 和 v-show 的区别是前者是当条件成立的时候才会渲染组件，并且条件不成立的时候会删除组件，等条件成立的时候再重新渲染，而后者则是一开始就渲染了组件，然后通过 css 的 ==display: none;== 来控制元素的显示与否。所以根据场景不同来选择使用这两个方法，当元素不需要重新渲染的时候应尽量使用 v-show，避免频繁渲染组件。</p>

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